1. Field of the Invention
The present invention relates to a pneumatic tire having a sidewall on which an outer surface has been patterned.
2. Background Information
In order to achieve a lighter weight and a lower rolling resistance in a pneumatic tire, the thickness (hereinafter also referred to as the side gauge) of the sidewall is continually being reduced. However, when the side gauge is reduced, there is a tendency for the surface of the sidewall to present an undesirable outer appearance. For example, uneven parts can form in local areas on the outer surface of the sidewall. The number of occurrences of other type of deficiencies in the sidewall may also increase. Although an undesirable outer appearance does not having adversely affect the durability or motion performance of the tire, a user may question whether or not such a tire is defective.
In the molding step performed during the manufacture of a tire, a sheet-shaped carcass member is wound once around a tire molding drum, and the originating and terminating ends of the wound carcass member partially overlap to form a joint. For this reason, the overlapped portion is of greater relative thickness, and takes on an uneven appearance on the outer surface of the sidewall in the tire. This unevenness is particularly noticeable in a radial tire for which a single carcass member is used.
Japanese Laid-open Patent Publication No. 2011-37388 describes a tire in which any unevenness occurring on the outer surface of the sidewall of the tire is obscured. On a decorative part extending as a strip in the circumferential direction of the pneumatic tire on the outer surface, a first ridge group and a second ridge group are formed. The first and second ridge groups are made of a plurality of ridges that are arranged so as to extend in the radial direction of the tire at a predetermined pitch. Each of the ridges of the first ridge group and each of the ridges of the second ridge group intersect with each other to form a moiré pattern which makes it possible to obscure any unevenness present on the outer surface of the sidewall.
Also, Japanese Laid-open Patent Publication No. 2008-273505 describes a pneumatic tire whose outer appearance can be enhanced by causing the light reflectance of the outer surface of the sidewall to vary. In this type of pneumatic tire, an uneven part is formed on at least a part of the outer surface of the sidewall. In the uneven part, recesses and protrusions are disposed in alternation, such that at least some of the recesses are made of a mirror surface having an arithmetic average surface roughness (Ra) of 0.4 to 1.5 μm, and a surrounding region that encloses the mirror surface is made of a rough surface where the Ra is greater than 1.5 μm.